[Bug target/67675] New: [SH] Improve __builtin_strcmp alignment test

["olegendo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67675

            Bug ID: 67675
           Summary: [SH] Improve __builtin_strcmp alignment test
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: olegendo at gcc dot gnu.org
  Target Milestone: ---
            Target: sh*-*-*

If the alignments of both input pointers to __builtin_strcmp are not at least 4
bytes, code is emitted to do a run-time check:

int foo1 (const char* x, const char* y)
{
  return __builtin_strcmp (x, y);
}

_foo1:
        mov     r4,r0
        or      r5,r0      // OR pointers
        tst     #3,r0      // check if both are 4 byte aligned
        bf.s    .L9

If one of the pointers is 4 byte aligned, the OR can be omitted, because we
need to check only one pointer's alignement.  For example:

int foo2 (const char* x, const char* y)
{
  return __builtin_strcmp (__builtin_assume_aligned (x, 4), y);
}

or also:

struct S
{
  int a, b, c;
  char s[64];    // this array will be always 4 byte aligned.
};

int foo4 (struct S* x)
{
  return __builtin_strcmp (x->s, "1234");
}